The investigators assume that Phenylephrine may decrease cardiac output by increasing the afterload, while most likely could also make an increase or a stability of cardiac output by action on the venous return. The investigators propose an observational study assessing the influence of preload dependence, defined by the values of pulse pressure variation, on the effect of phenylephrine on cardiac output, measured beat by beat by esophageal Doppler.

The aim of the investigators work is to improve the understanding of phenylephrine action, a daily use therapeutic action, to improve the patients care.

cardiac output [ Time Frame: one year ] [ Designated as safety issue: No ]

Comparing cardiac output values before and after injection of a phenylephrine bolus, based on the existence of a preload dependency, defined by a measure of respiratory variation of pulse pressure greater than or equal to 13%.

Injection of a bolus of phenylephrine at the discretion of the anesthesiologist physician in charge of the patient.

Exclusion Criteria:

Minor or major patient under guardianship

Esophageal Diseases

supra ventricular rhythm trouble

Severe valvular

Shunt intracardiac

Vt <7ml/kg theoretical weight

heart rate / respiratory rate <3.6

Clinical hypepression of intra-abdominal

Compliance <30 mL/cmH2O

pulmonary hypertension, Right ventricular failure

Spontaneous Ventilation

Thorax open

VG severe dysfunction (LVEF <40%)

Prior Injection of ephedrine prior

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Please refer to this study by its ClinicalTrials.gov identifier: NCT01730820